Several compounds related to the cephalosporin antibiotics and containing a
novel tricyclic beta -lactam system have been prepared in the expectation
that they might have a more strained beta -lactam ring than the parent comp
ounds. In the event, synthetic problems required that the compounds prepare
d containing this system had a reduced thiazine ring. The ring strain was n
ot exceptional as judged by the absorption frequencies in the infra red.